1. Field of the Invention
The invention relates to a tubular reinforcement member for a motor vehicle door.
2. Description of the Related Art
A reinforcement member of this type is known as disclosed in DE 40 32 992 A1. The reinforcement member serves as a stiffening particularly of the door of a passenger car and is intended to absorb the impact energy in the case of an impact from the side and to convert the impact energy into mechanical work. The desired result is an increased safety of the passengers of passenger cars, independently of whether another car impacts from the side or whether, for example, a passenger car whose driver has lost control impacts against a post or a mast.
In view of the fact that in the case of an impact the middle portion of the reinforcement member provides the greatest contribution to the magnitude of the capability of work absorption, it is suggested in the known case, by taking into consideration the known mathematical relationships between elastic line and section modulus, to provide the middle portion in longitudinal direction of the reinforcement member with a resistance against bending loads which is greater than that of the end portions serving for fastening the reinforcement member to the inner side of the door. For this purpose, the middle portion has not only been deformed into an elliptic or oval shape, but has additionally been provided with a metal sleeve which is slid into or onto the reinforcement member prior to the deformation of the middle portion. The sleeve is fixed into its position by gluing, welding or soldering. As an alternative to the sleeve which is closed at its circumference, additionally the use of a slotted sleeve has been suggested, wherein the sleeve is selected in its dimensions in such a way that a clamping effect occurs. Moreover, in accordance with a third alternative, the wall thickness in the middle portion is selected greater than in the adjacent portions or the inner space of the middle portion was filled with a medium, for example, a metal foam or wood, which has a lower specific gravity.
However, all of these measures for reinforcing the middle portion of a reinforcement member have in common that the manufacture is technically difficult and fixing it in its position is complicated. A very expensive individual manufacture of each reinforcement member is generally unavoidable.